Image morphing capability is increasingly becoming an important design consideration in electronic devices. In the optical and imaging arts, “morphing” refers to the changing of one image to another. For example, electronic devices frequently employ “morphing user interfaces,” i.e., interfaces that change in appearance as a device's use changes. Such an interface is simpler and more intuitive to use since only the context-relevant functions are shown at any given time, with the interface elements that are not related to the current context being inactive and hidden. A simple example of a morphing user interface is a screen through which display content is visible in one state, such as an “on” state, and not visible in another state, such as an “off” state. In the “off” state, a user may see, for example, a reflection of the ambient light incident on the screen.
Several known morphing techniques can achieve a change from a transparent state to a specular reflective (i.e., mirror-like) state, such as a change from the content typically seen on a cellular telephone display or touch-sensitive keypad area to a mirror-like image. U.S. Pat. No. 6,574,044 (“the '044 patent”) describes a combination of a reflective polarizer and a colored dichroic polarizer to achieve colored looks with a liquid crystal (“LC”) display. This construction can achieve specular reflective colors, but not diffusive colors. One embodiment of the '044 patent also employs a diffusive adhesive to achieve diffusive colors, but this embodiment cannot achieve switching between a transparent state and a diffusive state because as long as the diffusive adhesive is present, all incoming light is diffused under all circumstances.
U.S. Pat. No. 6,184,955 describes an LC device including a specular reflective polarizer and a light scattering layer. Because the light scattering layer is not polarization-sensitive, however, this construction does not enable switching between a transparent state and a diffusive state.
U.S. Patent Publication 2004/0036821 describes an LC shutter including at least two LC cells and at least three polarizers. The LC shutter may include scattering layers and reflective layers. However, this construction only describes the use of scattering layers to suppress interference effects in the LC shutter. The scattering layers are not polarization-sensitive and thus do not enable switching between a transparent and a diffusive state. This construction is also cumbersome because it uses two LC cells in the LC shutter.
Other known morphing constructions use a specular or diffusive reflective polarizer between the LC shutter and a light source, such as a display, for “recycling” purposes. The LC shutter typically passes light polarized along one direction and absorbs light polarized along a different direction. Such absorption of “wrongly-polarized” light is wasteful. Accordingly, the specular or diffusive reflective polarizer reflects wrongly-polarized light emanating from the light source and prevents it from being absorbed by the LC shutter. Another reflector placed on the opposite side of the light source reflects the light back, with a different polarization or polarizations, and provides another opportunity for the light to be transmitted. Thus, if a diffusive reflective polarizer is used in such a construction, it only provides “recycling” capability and does not enable the LC shutter to switch between a transparent state and a diffusive state.
Other constructions do provide for switching between a transparent state and a diffusive state, but are not polarization-sensitive LC shutters and therefore produce lower image integrity, along with lower transmission in the transparent state. For example, U.S. Pat. Nos. 6,760,157 and 6,590,705 describe optical films that provide diffuse reflection. However, the film is not included within a construction having other polarization-sensitive elements to optimize image integrity and the degree of transmission in the transparent state. For example, the diffuse reflection may be obtained by applying a voltage directly to the film itself to control the degree to which it is transparent to or scattering to incoming light.
Accordingly, it is desirable to provide electronic devices having the ability to switch between a transparent state and a diffusive state in a size- and cost-efficient manner, and that are polarization-sensitive and provide high image integrity and high transmission in a transparent state. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.